In conventional pumps or motors employing Moineau gear pairs, the inner member and the outer member move with respect to each other. If the outer member is held stationary, the inner member rotates and gyrates within the outer member. If the inner member is held stationary, the outer member rotates and gyrates with respect to the inner member. Since the outer element has a number of threads differing by one from the number of threads on the inner element, a series of pumping pockets is provided between the inner and outer elements, and these pockets move through the pump or motor in a helical path. The axes of the inner and outer members are parallel but displaced by an amount designated as the eccentricity of the pump or motor.
In one of the early Moineau U.S. Pat. No. 2,505,136, granted Apr. 25, 1950, it was taught that the inner member of the gear pair could rotate on its own axis without gyration, and the outer member was also free to rotate on its own axis, the axes being separated by the eccentricity of the pump. In this case, the pumping pockets, instead of traveling in a helical path, move straight through the pump axially.
The device of the Moineau U.S. Pat. No. 2,505,136 proved to be most inefficient. Because of the fact that both the inner and outer elements were rotating, the volume pumped by the pump was approximately one-half of what would be pumped by another conventional Moineau gear pair where one or the other of the gear elements was held stationary against rotation. Therefore, the device of this patent never went into use because of this inefficiency. While Moineau indicated in earlier patents that his devices could function as a pump if one of the gear elements was driven, he also indicated that it could function as a hydraulic motor if a liquid was pumped through the device. However, in the U.S. Pat. No. 2,505,136, Moineau did not discuss the possibility of using his device as a motor.
Because of this inefficiency, this patent turned out to be what might be referred to as a paper patent and never went into use and was forgotten.
In Clark U.S. Pat. No. 4,059,165, dated Nov. 22, 1977, there is taught a versatile fluid motor and pump which when two of the devices are coupled together make it possible to decrease the speed of the motor which is connected to the drill bit and thereby increase the torque. However, this requires the assembly of two hydraulic motors, as taught in that patent.
According to the present invention, the result of higher torque and decreased speed is accomplished with a single hydraulic motor.
If it were attempted to use directly the teachings of the Moineau U.S. Pat. No. 2,505,136, and use the device shown in FIG. 3 as a motor rather than a pump, the result would be very unsatisfactory because the drill bit would have to be secured to the member which is rotating on an axis central of the pipe 40, and this is the thinnest part of the device. Furthermore, the outer gear member 44 would be offset to one side of the pipe 40 which would create an unbalance and blockage of the annulus by a rotating wall contact and thus an entirely unsatisfactory device.